V. K. Voronov

Irkutsk State Technical University, 83 Lermontov Str., 664074, Irkutsk, Russia, voronov@istu.edu.ru

The present paper deals with the possibility of creation of the quantum com- puter in which the role of q-bits is played by quasi-particles. In such a computer, the elementary computation block should represent a cluster created on the basis of the paramagnetic molecules. The latter form heterogeneous spin states in the cluster owing to the presence of interelectron correlations.

Keywords: Quantum computer; strongly correlated systems; entangled states.

The quantum computer is a device which work should be described by parameters, typical for macroobjects. At the same time, the computa- tion procedure in such a device is based on the application of microob- jects which are in certain quantum states. According to modern notions, the case in point is quantum particles for which entangled states, detected on macrolevel, are possible. Importantly, such microparticles should be much enough in number that the quantum computer could solve the real tasks /1/. However it is easy to notice that the conditions indicated, in their turn, generate problems in the description of systems containing great number of quantum particles. In this connection, one might specify, at least, two problems. The first problem is due to the necessity of generation of entangled states. Initially, in the first years of investigations, this problem seemed to be solved by the employment of atom nuclei for this purpose. Some ad- vances have been made in this direction. In particular, the elementary quantum processor on the basis of the phenomenon of nuclear magnetic resonance (NMR) has been created /2,3/. However, a short time later, some basic difficulties have appeared here. They are related to the reali- zation of the entangled states (unambiguously detected on macrolevel) of system nuclear spins containing large number of non-equivalent atoms with respect to chemical environment /4/. It turned out that selective ac- tion on a specific nucleus inevitably produces the undesirable effect on states of other resonating nuclei. In this line, it has been proposed /5/ to use the system of q-bits, which would be in a superposition (relative to spin) state by the moment of action of the NMR impulse. It is pertinent to note that this system should attain such a state due to the evolution which is not connected with NMR action planned.

2 The second problem can be considered as a consequence of the properties caused by collective behavior of quantum particles participat- ing in the computation, in particular, by interelectron correlations if to steal about the system of electrons. The account of effects induced by this behavior is necessary, for example, to describe the properties of strongly correlated systems /6/. In these compounds, several degrees of freedom (spin, charge, spin-orbital, and photon) compete and interact. The investi- gations conducted over the last twenty years have shown that various physical phenomena are inherent for the compounds containing atoms with unoccupied − d 3 , − f 4 and − f 5 shells. In solid states, such atoms preserve completely or partially localized magnetic moments. A strong interaction of electrons with each other or with collectivized electrons of outer shells is a peculiarity which imparts unique properties to a series of compounds containing the atoms of transitive and rare-earth elements. If the interelectron correlations are essential elements of behavior of system with many quantum particles, it would be rational to try to use them for the realization of quantum computation procedure. In the work /7/, it has been shown that heterogeneous spin states may exist in hetero- spin systems, i.e. in coordination compounds of the paramagnetic ions in- corporating molecules bearing non-paired electrons as ligands. Since the magnetic and spin moments are interrelated, it is possible to say that in the molecules of the above-mentioned compounds, heterogeneous mag- netic states can appear owing to the interelectron correlations. The appearance of these heterogeneous spin states makes it possi- ble the electrons, localized in these states for some time, to be detected. For a certain time, an electron is placed to one of such states (for exam- ple, on − d orbital of the central ion). Owing to a specificity of in- tramolecular spin interactions, the electron is delocalized for some time into other state. Therefrom it is transferred again to the orbitals of metal. Then the cycle repeats. Thus, the state of entanglement, needed for the work of the quantum computer, is realized. Such state can preserve for any time, if the following condition is fulfilled:

( ) n bx ax x f −

, (1)

where a and
− b constant positive coefficients, 2